Hua said those who signed the letter were "extremely disrespectful" to people engaged in normal and friendly exchanges and cooperation between China and foreign countries, and also interfered with China's sovereignty and judicial affairs.

The two, Michael Spavor and Michael Kovrig, were detained in China in December for allegedly endangering national security.

Hua stressed that China welcomes foreign nationals, whether they are former diplomats, scholars or ordinary people, to come to China and engage in normal and friendly exchanges. There is nothing to worry about as long as they abide by Chinese laws and regulations, she added.